JP3317260B2 - Manufacturing method of round billet slab by continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a round billet slab by continuous casting, and more particularly to a method for producing a round billet slab for pipe making using a so-called unsolidification rolling and post-solidification molding method.

[0002]

2. Description of the Related Art When a round billet slab is manufactured by continuous casting, if the material of the round billet slab is low carbon steel, bearing steel or high Cr steel, segregation occurs at the center of the slab which solidifies last.
(Center segregation), casting defects such as cracks in the shaft core and porosity.

If a round billet slab having such a casting defect is used as it is in the production of a seamless pipe, an inner surface defect frequently occurs in the product due to the casting defect, and the product does not become a product.

Therefore, in order to suppress the casting defects of the round billet slab and improve the inner surface quality, there are a number of techniques for preventing the occurrence of casting defects by rolling down the cast continuous cast slab. Proposed. These techniques are referred to as unsolidification rolling and post-solidification molding methods.

For example, JP-A-10-249490 and JP-A-10-249490
According to Japanese Patent No. 144661, in both cases, the central portion of the continuous cast slab is subjected to a large pressure reduction (hereinafter, referred to as “unsolidified large pressure reduction” in the present specification) at a position of an unsolidified portion by a pair of horizontal rolls.
Thereafter, a method of forming and rolling into a perfect circle by using a pair of grooved vertical rolls is disclosed. According to these methods, the unconsolidated large pressure reduction is performed when the central portion is unsolidified, so that the concentrated molten steel in the central portion is flowed and discharged to the casting upstream side. Therefore, it is said that the center segregation of the round billet slab can be reduced and the center porosity can be eliminated.

[0006]

However, even if the rolling method proposed in these publications is applied to an actual continuous casting line, it is extremely difficult to perform unsolidified large rolling under normal rolling conditions. I understood.

[0007] That is, although JP-A-10-249490 and JP-A-10-146651 and the like do describe the amount of reduction to be set, the rolling conditions (roll load) for obtaining this amount of reduction are described. And roll torque) were not disclosed, it was difficult to determine the rolling conditions when applying to an actual continuous casting line. For this reason, it is actually not easy to perform unsolidified large pressure reduction.

Incidentally, in the conventional equipment, the load of the horizontal roll was about 40 tons, and the torque was about 2 tons-m. The load of the hole-shaped vertical roll was about 80 tons, and the torque was about 20 tons-m.

It is an object of the present invention to clarify rolling conditions under which a desired rolling reduction can be obtained when producing a round billet slab for pipe making using a so-called unsolidification rolling and post-solidification molding method. Accordingly, it is to reliably prevent the occurrence of casting defects in the round billet slab.

[0010]

Means for Solving the Problems The inventors of the present invention have studied to achieve this object, and have obtained the knowledge and findings listed below to complete the present invention.

JP-A-10-249490 and JP-A-10-14
In order to perform unsolidified large rolling reduction disclosed in, for example, US Pat. No. 6651, it is indispensable to set new rolling conditions that greatly exceed conventional conditions set for horizontal rolls and vertical rolls.

For example, in order to perform uniform rolling with a pair of grooved vertical rolls after performing unsolidified large pressure reduction with a pair of horizontal rolls, all of the horizontal rolls and the vertical rolls are used as drive rolls, and a slab is used. It is essential to equalize the stress acting on the

Here, the gist of the present invention is that a continuous cast slab having an unsolidified portion therein and having a substantially circular cross section is rolled down by one or more pairs of horizontal rolls. After making the cross section substantially elliptical, by rolling down with one or more pairs of hole-shaped vertical rolls, when manufacturing round billet slabs, (i) both the horizontal roll and the vertical roll, (Ii) the horizontal roll has a load of 50 tons or more and the torque is 3 ton-m or more, and (iii) the vertical roll has a load of 100 tons.
It is a method for producing a round billet slab by continuous casting, wherein the torque is 25 ton-m or more and the torque is 25 ton-m or more.

From another viewpoint, the present invention provides a method of rolling a continuous cast slab having an unsolidified portion therein and having a substantially circular cross section with one or more pairs of vertical rolls. After making the cross section substantially elliptical, by rolling down with one or more pairs of hole-shaped horizontal rolls, when manufacturing round billet slabs, (i) both vertical rolls and horizontal rolls, Drive rolls, (ii) vertical rolls have a load of 50 tons or more and torque of 3 ton-m or more, and (iii) horizontal rolls have a load of 100 ton or more and torque A method for producing a round billet slab by continuous casting, wherein the slab is 25 tons-m or more. In the present invention, the “transverse section” means a section substantially perpendicular to the length direction of the continuous cast slab.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for producing a round billet slab by continuous casting according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory view schematically showing a manufacturing process 10 of a round billet slab by continuous casting in the present embodiment. In FIG. 1, molten steel 3 poured from a tundish 1 into a continuous casting mold 2 having a circular horizontal cross-sectional shape is cooled in the mold 2 and a solidified shell is formed outside. An unsolidified portion remains inside the formed solidified shell.

The slab 4 drawn from the mold 2 enters the pinch roll zone 6 via the spray cooling zone 5. At this time, the cross-sectional shape of the slab 4 remains substantially circular. Then, the slab 4 having passed through the pinch roll band 6 is subjected to a large unsolidified pressure reduction by a pair of unsolidified reduction horizontal rolls 7, while the central portion remains unsolidified. The cast piece 4 which has been unsolidified and largely reduced by the pair of unsolidified reduction horizontal rolls 7 has a substantially elliptical cross-sectional shape.

Thereafter, the slab 4 is formed into a perfect circle by a pair of forming vertical rolls 8 provided in a region where the inside of the slab is completely solidified. In the illustrated example, only one pair of the pair of forming vertical rolls 8 and 8 is provided. However, if necessary, a plurality of stages such as a forming vertical roll and a forming horizontal roll may be provided alternately. In addition, after a plurality of vertical forming rolls, a plurality of horizontal forming rolls may be provided.

Further, in the present embodiment, the slab 4 is largely flattened down by the unsolidified rolling down horizontal rolls 7 and 7 and formed by the forming vertical rolls 8 and 8, but may be reversed. For example, a slab 4 is formed by a vertical roll under unsolidified pressing.
May be flattened to a large pressure and formed by a horizontal roll for forming. And the slab 4 is pulled out by a pinch roll 9.
To form a round billet slab 4 ′ for manufacturing a seamless pipe.

[0020] In order to eliminate the porosity and internal cracks and improve the internal quality of the slab 4, an extremely large reduction amount is required by performing the unsolidification large reduction using the pair of unsolidification reduction horizontal rolls 7,7. is necessary. The above-mentioned Japanese patent
According to Japanese Patent Application Laid-Open Nos. 10-249490 and 10-146651, it is understood that the amount of reduction under the unsolidified large pressure needs to be at least 30 mm.

FIG. 2 is a graph showing the results of examining the relationship between the amount of reduction (mm) and the load (ton) when the unsolidified large reduction is performed on the slab 4 by the unsolidified reduction horizontal roll 7. is there.
As shown in the graph, it is understood that in order to obtain a reduction amount of 30 mm or more, the load of the unsolidified reduction horizontal roll 7 needs to be 50 tons or more. Here, the load means a so-called rolling load, and acts as a force for crushing the slab 4.

FIG. 3 shows the amount of reduction (m) when unsolidified large reduction is performed on the slab 4 by the unsolidified reduction horizontal roll 7.
7 is a graph showing the result of examining the relationship between m) and torque (ton-m). As shown in the graph, it is understood that in order to obtain a reduction amount of 30 mm or more, the torque of the unsolidified reduction horizontal roll 7 needs to be 3 ton-m or more. here,
The torque is a force acting on and extruding the slab 4 and acts as a force for pulling out the slab 4.

In order to increase the load and torque of the unsolidified rolling horizontal roll 7 as in this embodiment, the rolling mechanism and the driving device of the unsolidified rolling horizontal roll 7 may be appropriately enhanced. Such enhancement is not limited to any particular means.

On the other hand, a large flat cast slab 4 is produced by performing a large unsolidification reduction by a non-solidification reduction horizontal roll 7.
A large facility capacity is also required when the steel sheet is rolled into a predetermined shape by the forming vertical roll 8.

FIG. 4 shows a slab 4 by a vertical roll 8 for forming.
7 is a graph showing the result of examining the relationship between flatness (%) and load (ton) when forming rolling is performed. In addition,
The flatness (%) is calculated from a flat cast slab by 長 (major axis−minor axis) / circular diameter｝ × 100. As shown in the graph, in order to perform the forming and rolling so that the slab 4 has a perfect circular shape with an allowable flatness (flatness: within 3%), the load of the forming vertical roll 8 is 100 tons. It turns out that it becomes necessary above.

FIG. 5 is a graph showing the result of examining the relationship between flatness (%) and torque (ton-m) when forming and rolling the slab 4 by the forming vertical roll 8. It is. As shown in the graph, in order to perform forming rolling so that the slab 4 has a perfect circular shape with an allowable flatness (flatness: within 3%), the torque of the forming vertical roll 8 is 25. It can be seen that more than ton-m is required.

As in the present embodiment, the forming vertical roll 8
In order to increase the load and torque of the vertical roll 8 for forming, the pressing mechanism and the driving device of the vertical roll 8 may be appropriately strengthened. Such enhancement is not limited to any particular means.

Further, if at least one of the unsolidified pressing horizontal rolls 7, 7 and the forming vertical rolls 8, 8 is a driven roll, the pulling force acting on the slab 4 is driven by the driven roll and the driven roll. The slab 4 becomes uneven on the roll side and bends toward the drive roll side. Therefore, a desired round billet cast piece 4 'cannot be obtained. Therefore, in the present embodiment, both the unsolidified pressing horizontal rolls 7, 7 and the forming vertical rolls 8, 8 are drive rolls.

According to this embodiment, since the rolling conditions for obtaining a desired reduction amount are clear, a round billet slab for pipe production is formed by using a so-called unsolidification reduction and post-solidification molding method to form a casting defect. It can be reliably manufactured while preventing the occurrence of slabs and bending of the slab. The outer diameter of the round billet slab 4 'obtained according to this embodiment is 400 mm or less.

[0030]

EXAMPLES The present invention will be described more specifically with reference to examples. Using a manufacturing process 10 shown in FIG. 1 having a continuous casting mold 1 having a circular cross section having a diameter of 225 mm, a 225 mm diameter carbon steel having a C content of 1.0% by weight was used.
Was continuously cast at a casting speed of 1.5 m / min.

In FIG. 1, a horizontal roll 7 under unsolidified pressure is used.
The position where the non-solidification large reduction was performed by 7 was 23 m from the melt meniscus, and the position where the forming and rolling were performed by the vertical forming rolls 8 and 8 was 32 m from the melt meniscus. The spray cooling specific water amount in the spray cooling zone 5 was 0.10 l / kg · steel.

Then, as shown in Table 1, the load and torque of the unsolidified rolling down horizontal roll 7 and the forming vertical roll 8 and the driving state of each of the unsolidified rolling down horizontal roll 7 and the forming vertical roll 8 are changed. Then, the presence or absence of internal cracks, flatness (%) of the obtained round billet slab 4 ′,
And the presence or absence of slab bending was examined. The results are shown in Table 1 together with the evaluation of the round billet slab 4 '.

[0033]

[Table 1]

In Table 1, Example 1 shows that the horizontal roll 7 under unsolidification pressure: load 50 tons, torque 3 tons-m, vertical roll 8 for forming: load 100 tons, torque 25 tons-m,
Each roll is a drive roll. Therefore, the round billet slab 4 'was satisfactory without any internal cracks, flatness and slab bending.

In Example 2, a horizontal roll 7 under unsolidified pressure: a load of 100 tons, a torque of 15 tons-m, and a vertical roll for forming 8:
The load is 200 tons, the torque is 50 tons-m, and each roll is a driving roll. Therefore, the round billet slab 4 'was satisfactory without any internal cracks, flatness and slab bending.

In Example 3, a horizontal roll 7 under unsolidified pressure: a load of 150 tons, a torque of 30 tons-m, and a vertical roll for forming 8:
The load is 300 tons, the torque is 75 tons-m, and all the rolls are drive rolls. Therefore, the round billet slab 4 'was satisfactory without any internal cracks, flatness and slab bending.

Further, in Example 4, the horizontal roll 7 under unsolidified pressure: load 200 tons, torque 50 tons-m, vertical roll 8 for forming: load 400 tons, torque 100 tons-m, all rolls being driven Roll. Therefore, the round billet slab 4 'was satisfactory without any internal cracks, flatness and slab bending.

On the other hand, in Comparative Example 1, the loads and torques of the unsolidified pressing horizontal roll 7 and the forming vertical roll 8 are insufficient, and one of the rolls is a driven roll. For this reason, the round billet slab 4 'had internal cracks, the flatness exceeded the allowable value, and the slab was bent. For this reason, both the quality and the operation were unsatisfactory.

In Comparative Example 2, one of the horizontal rolls 7 under unsolidified pressure is a driven roll, and the load and torque of the forming vertical roll 8 are both insufficient and one is a driven roll. For this reason, the round billet slab 4 'had a flatness exceeding the allowable value and the slab was bent. For this reason, both the quality and the operation were unsatisfactory.

In Comparative Example 3, the load and torque of the horizontal roll 7 under unsolidified pressure were both insufficient and one was a driven roll, and one of the forming vertical rolls 8 was a driven roll. As a result, the round billet slab 4 'had internal cracks and the slab was bent. For this reason, both the quality and the operation were unsatisfactory.

In Comparative Example 4, since both the unsolidified pressing horizontal roll 7 and the forming vertical roll 8 had insufficient load and torque, the round billet cast piece 4 'had internal cracks,
The flatness also exceeded the allowable value. For this reason, both the quality and the operation were unsatisfactory.

Further, in Comparative Example 5, one of the horizontal roll 7 under unsolidified pressure and the vertical roll 8 for forming is a driven roll. For this reason, the round billet slab 4 'was bent and the operation was unstable.

[0043]

As described above in detail, according to the present invention, when a round billet slab for pipe making using a so-called unsolidification rolling and post-solidification molding method is manufactured, a desired reduction amount can be obtained. By clarifying the rolling conditions to be obtained, a round billet slab having good internal quality and good external surface shape can be obtained while reliably preventing the occurrence of casting defects. The significance of the present invention having such an effect is extremely remarkable.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a manufacturing process of a round billet slab by continuous casting in an embodiment.

FIG. 2 is a graph showing the result of examining the relationship between the amount of reduction (mm) and the load (ton) when performing unsolidified large reduction on a slab by an unsolidified reduction horizontal roll.

Fig. 3 Reduction amount (mm) and torque (ton-m) when performing unsolidification large reduction on a slab by unsolidification reduction horizontal rolls
6 is a graph showing the result of examining the relationship with.

FIG. 4 is a graph showing a result of examining a relationship between flatness (%) and load (ton) when forming and rolling a slab using a vertical forming roll.

FIG. 5 is a graph showing a result of examining a relationship between flatness (%) and torque (ton-m) when forming and rolling a slab by a vertical forming roll.

[Explanation of symbols]

 Reference Signs List 2 mold 4 cast slab 4 'round billet slab 6 pinch roll band 7 unsolidified pressing horizontal roll 8 forming vertical roll 9 pulling pinch roll

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-328800 (JP, A) JP-A-10-175049 (JP, A) JP-A-10-52744 (JP, A) JP-A-10- 193064 (JP, A) JP-A-10-146651 (JP, A) JP-A-10-249490 (JP, A) JP-A 2000-153349 (JP, A) JP-A 2001-126855 (JP, A) JP-A-11-179509 (JP, A) JP-A-9-201691 (JP, A) JP-A-10-166124 (JP, A) JP-A-7-108358 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) B22D 11/00 B22D 11/128 340 B22D 11/128 350

Claims (2)

(57) [Claims] 1. A continuous cast slab having an unsolidified portion therein and having a substantially circular cross section is reduced by one or more pairs of horizontal rolls to make the cross section substantially elliptical. By rolling down with one or more pairs of hole-shaped vertical rolls to produce a round billet slab, (i) the horizontal roll and the vertical roll are both drive rolls, ) The horizontal roll has a load of 50 tons or more and a torque of 3 tons-m or more;
ii) A method for producing round billet cast pieces by continuous casting, wherein the vertical roll has a load of 100 tons or more and a torque of 25 tons-m or more. 2. A continuous cast slab having an unsolidified portion therein and having a substantially circular cross section is reduced by one or more pairs of vertical rolls to make the cross section substantially elliptical. By rolling down with one or more pairs of hole-shaped horizontal rolls to produce a round billet slab, (i) the vertical roll and the horizontal roll are both drive rolls, (ii) ) The vertical roll has a load of 50 tons or more and a torque of 3 tons-m or more;
ii) A method for producing round billet cast pieces by continuous casting, wherein the horizontal roll has a load of 100 tons or more and a torque of 25 tons-m or more.